Impatiens suksathanii Ruchis. & Triboun, 2014

Ruchisansakun, Saroj, Triboun, Pramote & Jenjittikul, Thaya, 2014, A new species of Impatiens (Balsaminaceae) from Southwestern Thailand, Phytotaxa 174 (4), pp. 237-241 : 237-240

Impatiens suksathanii Ruchis. & Triboun , sp. nov. ( Figs. 1 , 2 )

Impatiens suksathanii Ruchis. & Triboun is clearly distinguished from the most similar I. namkatensis T.Shimizu by having sessile to very short petioles, linear, narrowly lanceolate to narrowly oblanceolate laminas,and pale pink flowers.

Type:— THAILAND. Kanchanaburi: Thong Phaphum district, Wat Tha Khanun , on limestone rock, ca. 120 m elevation, 5 August 2008, Suksathan et al. 4325 (holotype BK, isotype QBG) .

Lithophytic, annual, glabrous herbs. Stems erect, 15–45 cm tall, up to 7 mm in diam., solitary or with many branches near the basal parts, each branch 5–15 cm long, upper part slender and zigzag, swollen at nodes, lower part larger and robust, pale to dark red. Leaves alternately arranged; petioles sessile, up to 3 mm long, 1–1.5 mm in diam., dark red; laminas linear, narrowly lanceolate to narrowly oblanceolate, 5–9 × 0.5–1.7(–2.2) cm, apex acute, base attenuate to cuneate, margin shallowly crenate, green, with a short red, stalked gland on each side of margin at 1/3–1/2 from the base, lateral veins 4–5 on each side of midrib. Inflorescences axillary, in 1–3-flowered fascicles, aggregated on the upper part of the branch; peduncles short, 1–1.5 mm long. Flowers pale pink, ca. 1 cm long; pedicels slender, 0.9–1.1 cm long, less than 0.5 mm in diam., pale green or pink with red dots on the upper side. Bracts narrowly triangular, ca. 1.5 × 0.4 mm, apex acute, pale green. Sepals 5, the outer pair free, obliquely ovate, 2–3 × 1–2 mm, apex acute to acuminate and mucronate, base obtuse, white to pale pink with green tips, one median vein obscure; the inner pair strongly reduced; the lower one bucciniform, 5–5.5 × 2.5–4 mm, ca. 4 mm deep, white to pinkish white with fine purple tessellate veins, distal part abruptly constricted into an entirely incurved spur, 3–5 mm long, green, tip brownish red, blunt. Petals 5; dorsal one oblanceolate to obovate, ca. 5 × 2.5–3 mm, purple with a green tip, strongly reflexed in the upper half, apex mucronate, base cuneate with a greenish brown crest; lateral united petals connate; the upper pair broadly triangular, ca. 1.5 × 5 mm, reflexed just above the base, apex acute or tridentate, base stipitate, pink with white and red dots; the lower pair connate, obovate in outline, 5–6 × 2.5–3 mm, apex truncate or shallowly emarginate, pink with darker strips at the base. Stamens 5; filaments flat, 1.5–2 mm long, white; anthers white. Ovary 4-carpellate, 1.5–2 mm long, ca. 1 mm in diam., green, glabrous. Capsules freshly dehiscent, clavate, 0.7–1 cm long, ca. 2 mm in diam., 4-lobed. Seeds 4–6, ellipsoid, ca. 2 × 1 mm, brownish orange with red pustules.

Phenology:— Flowering July to October.

Distribution:— Endemic to Southwestern Thailand (Kanchanaburi province).

Ecology:— Growing in crevices on open limestone cliffs, 100–400 m elevation.

Proposed IUCN conservation assessment:— Critically Endangered (CR B2 ab(iii,v)) following the criteria of IUCN (2012). This species is only known from two small populations from two localities, neither of which currently has any formal protected status. One locality is in the grounds of a temple in Thong Phaphum district that receives a lot of visitors and the other one is in the grounds of a university. Moreover, the entire population is estimated to contain fewer than 100 individuals.

Etymology:— The plant is named in a honour of Dr. Piyakaset Suksathan, an outstanding plant taxonomist from Queen Sirikit Botanic Garden in Thailand who has been working on the family Balsaminaceae for the Flora of Thailand for a decade. He also encouraged the first author to start his phylogenetic study on the genus Impatiens for his Master’s degree.

Additional specimens examined (paratypes):— THAILAND. Kanchanaburi: Sai Yok district , Mahidol University , Kanchanaburi campus, growing naturally on small limestone hills in the campus, 6 August 2011, Ruchisansakul 210 ( BK) ; Thong Phaphum district , Wat Tha Khanun , 5 August 2012, Middleton et al. 5255 ( BK, BKF, E) ; ibid., 4 December 2005, Pooma et al. 5859 ( BKF 163999 ) ; ibid., 21 August 2005, Ruchisansakul 215 ( BK) .

Notes:— Impatiens suksathanii Ruchis. & Triboun is one of the smallest-flowered Impatiens species in Thailand and belongs to subgenus Semeiocardium (Zoll.) N.Utami ( Utami 2009) with 4-carpellate ovaries and connate lateral united petals. This new species is closely related to I. namkatensis T.Shimizu ( Shimizu 2000: 37) , a northern Thailand endemic, but differs from it in having sessile to very short petioles (up to 3 mm long), linear, narrowly lanceolate to narrowly oblanceolate laminas, and pale pink flowers ( Table 1). The new species also has similarities to two Indian species, I. rosea Lindl. ( Lindley 1841: 27) and I. scabriuscula B.Heyne (in Roxburgh 1824: 464) but can clearly be distinguished from the first species by having a much smaller habit (up to 45 cm vs up to 150 cm tall), a glabrous stem, an un-horned apex to the dorsal petal, and glabrous lateral sepals (vs hairy along margins and mid-vein). From I. scabriuscula it can be distinguished by having an un-horned apex to the dorsal petal, a lower sepal with a distinct spur (vs no spur) and glabrous flowers and fruits. Also, both Indian species have a 5-carpellate ovary and free lateral united petals ( Table 1).

Figures

FIGURE 1. Impatiens suksathanii Ruchis. & Triboun. A. Habit in limestone crevices at the type locality; B. Detail of a branch with flowers. Photos by Saroj Ruchisansakun.

FIGURE 2. Impatiens suksathanii Ruchis. & Triboun. A. Habit; B–C. Flowers; D. Outer lateral sepals; E. Lower sepal; F. Dorsal petal; G. Lateral united petals; H. Fruit (B–H. share the same scale bar). Drawn by Saroj Ruchisansakun.